Reaction of beta platinum chloride with gaseous ammonia

ABSTRACT

This invention relates to reactions of beta platinum chloride with gaseous ammonia to yield metallic platinum useful in catalysis and other operations and also complexes of beta platinum chloride and ammonia, which complexes are considered to be new compositions and which are contemplated as being useful in cancer research.

This is a continuation, of application Ser. No. 532,445, filed Dec. 13,1974, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to reaction of beta platinum chloride withgaseous ammonia to yield metallic platinum or useful addition complexescharacterized by the formula PtCl₂ · X NH₃ where X is greater than zeroup to about 2.

2. Description of the Prior Art

It has been reported by W. Peters In Z. Anorg. Chem. 77 (1912) p. 137 etseq. that PtCl₂, prepared from thermally decomposing chloroplatinincacid, reacts with gaseous ammonia to produce a compound PtCl₂ · 5NH₃. Incarrying out such reaction, Peters exposed anhydrous PtCl₂ to ammoniavery slowly and maintained the solid at approximately room temperatureby regulating the flow of ammonia. The material prepared by Peters isdistinct from the compounds described herein. Insofar as is known, thereduction of beta platinum chloride with gaseous ammonia to yieldmetallic platinum, which offers a convenient method for synthesis ofsupported platinum metal catalysts, has not been reported.

Crystalline platinum compounds having the empirical formulae Pt(NH₃)Cl₂and cis and trans Pt(NH₃)₂ Cl₂ have been respectively reported by Kerret al. Inorg. Chem., 13 2294 (1974) and Watt et al. Journal ofElectrochem. Soc. 110, 716 (1963). The compounds described herein formedby the direct reaction of beta platinum chloride and ammonia gascharacterized by the same empirical formulas but different crystallinestructure or the absence of crystallinity, e.g., amorphous solids, havenot been reported.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has been found that betaplatinum chloride can conveniently be prepared by thermal decompositionof chloroplatinic acid in flowing air or an inert gas atmosphere andsubsequently reacted with gaseous ammonia to yield metallic platinum oraddition complexes having a composition represented by the formula PtCl₂· X NH₂ where X is a number greater than zero but not greater than about2.

Platinum chloride is known to exist in two different crystalline forms,namely alpha and beta. The structure of the alpha form has not beenpublished. The beta form contains discrete Pt₆ Cl₁₂ units and isvolatile. Beta platinum chloride can readily be synthesized bydecomposing chloroplatinic acid at a temperature in the range of 275°to450° C. in air or an inert gas such as nitrogen, argon or helium.Decomposition is believed to proceed typically in accordance with thefollowing equation:

    (H.sub.3 O).sub.2 PtCl.sub.6 · 2.3 H.sub.2 O → β-PtCl.sub.2 + 2Cl.sub.2 + 4.3 H.sub.2 O + 2HCl

The beta platinum chloride so produced is, in accordance with theprocess of the invention, contacted with gaseous ammonia, suitably atabout room temperature, e.g., about 25° C. A highly exothermic reactiontakes place with the formation of a white powder identified as ammoniumchloride. The temperature is then raised to about 400° C. during whichconsiderable weight loss occurs over the range of 200° to 375° C. Thefinal sample weight was that calculated for reduction of platinumchloride to metallic platinum. X-ray diffraction analysis confirmed thatthe final sample was metallic platinum. The reaction is believed toproceed in accordance with the following equation:

    3β-PtCl.sub.2 + 8 NH.sub.3 → 3 Pt + 6 NH.sub.4 Cl + N.sub.2

the vigorous reduction of beta platinum chloride with ammonia issurprising in view of its rather inert nature. This, it is known thatbeta platinum chloride is not readily soluble in water and essentiallyinsoluble in benzene, chloroform, ethanol, acetone and acetic acid. Incontrast to the ease of reduction of beta platinum chloride with ammoniato metallic platinum, it has been found that palladium chloride (PdCl₂)undergoes no reaction with ammonia at room temperature therebyindicating the much greater ease of reduction of PtCl₂ as compared withPdCl₂.

The above reaction of beta platinum chloride and gaseous ammonia may becarried out at a temperature between about 0° and about 450° C. andpreferably between about 20° and about 300° C. As a practicalembodiment, conduct of the reaction at approximately room temperature,i.e., about 25° C., is particularly preferred. Pressure during thereaction is within the range of about 0.5 to about 100 atmospheres, withapproximately atmospheric pressure being preferred. The molar ratio ofgaseous ammonia to beta platinum chloride is generally within the rangeof about 5 to 10 moles of NH₃ per mole of β PtCl₂.

When the pressure of ammonia is reduced to appreciably less than 0.5atmosphere, i.e., in the approximate range of 0.05 to 0.3 atmosphere andpreferably between about 0.1 and about 0.2 atmospheres, the betaplatinum chloride reacts slowly with the ammonia at a temperaturebetween about 0° and about 200° C. and preferably between about 20° andabout 100° C. to form products whose compositions can be defined by theformula:

    PtCl.sub.2 · X NH.sub.3

where X is a number greater than 0 but not greater than about 4. Theammonia in the described complexes is chemically bound and notreversibly sorbed. Thus, the ammonia in PtCl₂ · NH₃ is irreversiblyreacted. Heating this solid at 200° C. for as long as 16 hours gave nochange in composition. Heating above about 230° C. led to decompositionaccording to the reaction:

    2 PtCl.sub.2 · NH.sub.3 → 2 Pt + N.sub.2 + 4 HCl + H.sub.2

the X-ray diffraction pattern of the solid PtCl₂ · NH₃ shows the sameX-ray diffraction pattern as β-PtCl₂, i.e., the crystalline structure ofβ-PtCl₂ is retained. Apparently, the structure of β-PtCl₂ is open enoughto accommodate up to 1 molecule of NH₃ per Pt atom. This diffractionpattern is distinct from that of the reported monoamine Pt(NH₃)Cl₂prepared by the decomposition of trans Pt(NH₃)₂ Cl₂. Exposing the solidPtCL₂ · NH₃ to NH₃ gas up to 1 atmosphere pressure does not result in astrongly exothermic reaction. On the contrary, a slow uptake of NH₃takes place. The uptake of ammonia is constant and continuous until acomposition having the formula PtCl₂ · 2 NH₃ is obtained. The ammoniauptake continues yielding PtCl₂ · 3 NH₃ but at a decreasing rate as thecomposition approaches PtCl₂ · 4 NH₃. The X-ray powder diffractionpattern of the compound PtCl₂ · 2 NH₃ showed that it was amorphous, incontrast to the previously reported cis and trans Pt(NH₃)₂ Cl₂. Thesolids having the compositions PtCl₂ · 3 NH₃ and PtCl₂ · 4 NH₃ obtainedby the above procedure show the same X-ray powder diffraction patternsas the known complexes Pt(NH₃)₃ Cl₂ and Pt(NH₃)₄ Cl₂, although theselatter compounds have not previously been prepared as a result ofammoniation of the amorphous PtCl₂ · 2 NH₃.

The compounds PtCl₂ · X NH₃ above-described where X is greater than zerobut not greater than about 2 are considered new compositions andcontemplated as being useful in cancer research. It is known thatplatinum ammine chlorides, i.e., Pt(NH₃)₂ Cl₂, Pt(NH₃)₃ Cl₂ and Pt(NH₃)₄Cl₂ are of interest in cancer chemotherapy. The platinumchloride-ammonia complexes of this invention having the formula PtCl₂ ·X NH₃ where X is greater than zero but not greater than about 2 differfrom these previously known platinum ammine chlorides. Contact of thecis- and trans Pt(NH₃)₂ Cl₂ with gaseous NH₃ at room temperature and 1atmosphere pressure exhibited no reaction, further showing that PtCl₂ ·2 NH₃ differs from these known isomers.

The described reduction of beta platinum chloride with ammonia to yieldmetallic platinum may desirably be effected in the presence of a porousrefractory solid to yield supported platinum catalysts. Representativeporous refractory solids include charcoal, graphite, clays, inorganicoxides such as those composed predominantly of silica and/or alumina orcombinations of these oxides with oxides of the other elements. Otherinorganic oxides may include titania, germania, zirconia, magnesia, aswell as the oxides of calcium, nickel, cobalt, molybdenum or variouscombinations thereof. A particularly feasible catalyst made using thedescribed technique is one where the platinum is deposited on a supportcomprising predominantly alumina. Such support may have combinedtherewith, minor proportions of halogens, e.g., chlorine and/or fluorineto yield platinum-containing catalysts suitable for the reforming,hydrogenation, isomerization or dehydrocyclization of petroleumhydrocarbons. Such catalyst may also contain a metal other thanplatinum, such as rhenium, inidium, gold, zinc, and the like introducedonto the support either before, after or during compositing of thesupport with platinum utilizing the technique described hereinabove.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The following examples will serve to illustrate the invention andvarious embodiments thereof:

EXAMPLE 1

Four grams of H₂ PtCl₆ · 4.3H₂ O were placed in an alumina container andheated to 300° C. over 4 hours in a helium gas purge. The purge gas ratewas 200 cc/minute. The resulting product was identified as beta platinumchloride. The yield of β-PtCl₂ was 2.2 grams.

A small quantity (0.25 gram) of the beta platinum chloride prepared asdescribed above was contacted with a stream of ammonia gas. Animmediate, vigorous reaction occurred with a puff of white smoke. Theblack residue resulting from such reaction was determined by X-raydiffraction analysis to be metallic platinum.

EXAMPLE 2

A reaction between beta platinum chloride and gaseous ammonia similar tothat described in Example 1 was carried out on the balance pan of athermogravimetric analyzer. A thermocouple was located about 5 mm. fromthe sample. The thermocouple showed a very large temperature riseoccurred during the reaction to yield metallic platinum.

EXAMPLE 3

Using the thermogravimetric analyzer apparatus referred to in Example 2,a small sample (0.025 gram) of beta platinum chloride was contacted withan ammonia gas stream diluted with helium to about 0.1 chloride. Thebeta platinum chloride sample gained weight continuously with a small,i.e., 5° C. temperature rise observed with the thermocouple. When thesample weight corresponded to the composition PtCl₂ · NH₃, the ammoniawas discontinued and sample removed from the apparatus. X-raydiffraction pattern, i.e., the same crystal structure as beta platinumchloride. Larger amounts of samples of varying NH₃ content are preparedin a tube by passing dilute NH₃ in nitrogen over β-PtCl₂ for varyingtimes.

EXAMPLE 4

An approximately 2 gram sample of beta platinum chloride was contactedat room temperature in a tube with an ammonia gas stream diluted withhelium to about 0.1 atmosphere for about 50 minutes to yield a producthaving the composition corresponding to PtCl₂ · 2 NH₃. X-ray diffractionanalysis of this product showed the same to be amorphous.

EXAMPLE 5

Ten grams of eta-alumina were impregnated with 15 ml. of water to which0.125 gram of H₂ PtCl₆ was added. The resulting catalyst was then driedat 100° C. for 3 hours, followed by air calcination for 16 hours at 200°C. and 7 hours at 300° C. yielding beta platinum chloride. The catalystwas then contacted with gaseous ammonia at 300° C. for 15 minutes toyield a platinum-containing catalyst.

EXAMPLE 6

The catalyst prepared as in Example 5 was tested for reforming activity.An isothermal micropressure unit was employed. The feedstock was a C₆-200° F. naphtha. The reforming test was conducted at a temperature of900°-930° F., a pressure of 200 psig at a liquid hourly space velocityof 4 in the presence of hydrogen at a 15:1 hydrogen to hydrocarbonratio. The results obtained are shown in the table below.

    ______________________________________                                        Component          Temp. ° F.                                          (Wt. Percent)      900             930                                        ______________________________________                                        Time On Stream (Hr.)                                                                             17              41                                         C.sub.1                                                                                          1.1             3.1                                        C.sub.2                                                                       C.sub.3            1.3             3.4                                        iso C.sub.4        1.1             2.8                                        n-C.sub.4          0.8             2.1                                        iso C.sub.5        1.7             3.7                                        n-C.sub.5          1.6             2.5                                        2,2, Dimethyl C.sub.4                                                                            2.0             1.8                                        Cyclo C.sub.5                                                                                    1.1             1.1                                        2,3, Dimethyl C.sub.4                                                         2 Methyl C.sub.5   12.6            12.3                                       3 Methyl C.sub.5   8.2             7.8                                        n-C.sub.6          13.1            10.0                                       2,2 Dimethyl C.sub.5               0.2                                        Methyl Cyclo C.sub.5                                                                             4.8             1.4                                        2,4, Dimethyl C.sub.5              0.4                                        Benzene            12.4            14.9                                       3,3 Dimethyl C.sub.5                                                                             0.7             0.4                                        Cyclo C.sub.6      0.1             --                                         2 Methyl C.sub.6   4.6             2.7                                        2,3 Dimethyl C.sub.5                                                                             1.6             1.0                                        1,1 Trans, Dimethyl Cyclo C.sub.5                                                                0.1             --                                         3 Methyl C.sub.6   5.6             3.2                                        1,3 Trans, Dimethyl Cyclo C.sub.5                                                                0.7                                                        1,3 Cis, Dimethyl Cyclo C.sub.5                                                                  0.1             0.8                                        1,2 Trans, Dimethyl Cyclo C.sub.5                                                                0.3                                                        n-C.sub.7          4.5             2.3                                        1,2 Cis Dimethyl Cyclo C.sub.5                                                Methyl Cyclo C.sub.6                                                                             0.5             0.3                                        Ethyl Cyclo C.sub.5                                                           Toluene            17.5            19.4                                       C.sub.8.sup.+      1.9             2.4                                        C.sub.5.sup.+      95.7            88.6                                       C.sub.5.sup.+ (R+O)                                                                              76.0            83.4                                       ______________________________________                                    

From the above results, it will be seen that the manner of reducing betaplatinum chloride with ammonia in the presence of a porous support suchas alumina is a feasible method for producing an effective reformingcatalyst.

We claim:
 1. A method for preparing a complex having the formula: PtCl₂· X NH₃ in which ammonia is irreversibly reacted and where X is a numbergreater than 0 but not greater than essentially 2; and when X is 1, thecomposition has an X-ray diffraction pattern which is the same as betaplatinum chloride and distinct from the monoamine Pt(NH₃)Cl₂, preparedby the decomposition of trans Pt(NH₃)₂ Cl₂ ; and when X is 2 thecomposition is amorphous in contrast to the crystalline platinumcompounds having the empirical formula cis and trans Pt(NH₃)₂ Cl₂ ;which comprises reacting beta platinum chloride with gaseous ammonia ata temperature between about 0° and 200° C. at an ammonia pressure in theapproximate range of 0.05 to 0.3 atmospheres, and subsequentlyrecovering said complex.
 2. The method of claim 1 wherein thetemperature is between about 20° and about 100° C.
 3. The method ofclaim 1 wherein the temperature is approximately room temperature.